This work aims the deterministic dynamic analysis,in the time and frequency domain,of a reinforced concrete floor supported by a pre-cast pile foundation system,when subjected to the excitation produced by a large com...This work aims the deterministic dynamic analysis,in the time and frequency domain,of a reinforced concrete floor supported by a pre-cast pile foundation system,when subjected to the excitation produced by a large compressor installed in an industry for the production of air gases.The concrete slab presents a dimension of 12 m×15 m,required to support a compressor-motor assembly weighting 1,900 kN and positioned at a height of 4m of the investigated concrete floor.In this investigation,two numerical models were developed and the difference between these models is characterized by the discretization of the support points(pre-cast concrete piles).The developed numerical model adopted the usual mesh refinement techniques present in finite element method simulations implemented in the CSi SAP2000 V.17.2.0 software.Based on the developed analysis methodology,the dynamic structural response of the foundation system is evaluated in terms of natural frequencies,vibration modes,displacements,velocities,and accelerations.The maximum values of the dynamic response of the system are compared with the limit values recommended by standards and project recommendations,aiming a careful evaluation,regarding the performance of the structure in terms of excessive vibrations and the economic aspects involved in the design of the foundation system.Finally,the obtained results of the two developed numerical models are compared,as to evaluate if there are benefits in refining the support points modelling.展开更多
Purpose of present work is to develop a reliable and simple method for structural analysis of RC Shear Walls. The shear wall is simulated by a truss model as the bar of a truss is the simplest finite element. An itera...Purpose of present work is to develop a reliable and simple method for structural analysis of RC Shear Walls. The shear wall is simulated by a truss model as the bar of a truss is the simplest finite element. An iterative method is used. Initially, there are only concrete bars. Repeated structural analyses are performed. After each structural analysis, every concrete bar exceeding tensile strength is replaced by a steel bar. For every concrete bar exceeding compressive strength, first its section area is increased. If this is not enough, a steel bar is placed at the side of it. For every steel bar exceeding tensile or compressive strength, its section area is increased. After the end of every structural analysis, if all concrete and steel bars fall within tensile and compressive strengths, the output data are written and the analysis is terminated. Otherwise, the structural analysis is repeated. As all the necessary conditions (static, elastic, linearized geometric) are satisfied and the stresses of ALL concrete and steel bars fall within the tensile and compressive strengths, the results are acceptable. Usually, the proposed method exhibits a fast convergence in 4 - 5 repeats of structural analysis of the RC Shear Wall.展开更多
Lunar soil simulants(LSS)have been pivotal in the success of past and current lunar missions.They have enhanced the design of lander and rover wheels through interaction studies on the lunar testbed under simulated en...Lunar soil simulants(LSS)have been pivotal in the success of past and current lunar missions.They have enhanced the design of lander and rover wheels through interaction studies on the lunar testbed under simulated environmental conditions.They have also been used to evaluate the geotechnical,geomechanical,and dynamic characteristics of the lunar soil(LS),which is vital for future lunar outposts.While most simulants have focused on either the chemical and mineralogical or geotechnical properties,developing a comprehensive LSS that mimics the lunar soil is of paramount importance for lander and rover soft-landing and future lunar habitation.This article presents the significant development and characterization of the new LSS NYUAD-1,the first regional soil simulant tailored for the planned Emirates lunar missions.The material and geotechnical properties of NYUAD-1,including chemical composition,mineralogy,particle size,morphology,specific gravity,density,shear strength,and compressibility behaviors,were assessed through laboratory tests conducted per ASTM standards.Comparative analysis with authentic lunar regolith and various regolith simulants confirms the significance and applicability of NYUAD-1 for lunar-based research,offering a promising step toward future lunar habitation.展开更多
A dynamic analysis of both twisting and regular towers is carried out to determine the results of considering soil-structure interaction(SSI)on high-rise buildings.In addition,the difference between the seismic perfor...A dynamic analysis of both twisting and regular towers is carried out to determine the results of considering soil-structure interaction(SSI)on high-rise buildings.In addition,the difference between the seismic performance of using twisting towers over regular ones is investigated.The twisting tower is a simulation of the Evolution Tower(Moscow).The towers’skeletons consist of RC elements and rest on a reinforced concrete piled-raft foundation.The soil model is considered as multi-layered with the same soil properties as the zone chosen for the analysis(New Mansoura City,Egypt).The only difference between both towers is their shape in elevation.The whole system is modelled and analyzed in a single step as one full 3D model,which is known as the direct approach in SSI.All analyses are carried out using finite-element software(Midas GTS NX).Dynamic output responses due to three records of seismic loads are proposed and presented in some graphs.Based on the results,it is concluded that SSI has a considerable effect on the dynamic response of tall buildings mainly because of the foundation flexibility,as it leads to lengthening the vibration period,increasing the story drift and the base shear for both cases.展开更多
In this paper, the hydrodynamic efficiency of a floating breakwater system is experimentally studied by use of physical models. Regular waves with wide ranges of wave heights and periods are tested. The efficiency of ...In this paper, the hydrodynamic efficiency of a floating breakwater system is experimentally studied by use of physical models. Regular waves with wide ranges of wave heights and periods are tested. The efficiency of the breakwater is presented as a function of the wave transmission, reflection, and energy dissipation coefficients. Different parameters affecting the breakwater efficiency are investigated, e.g. the number of the under connected vertical plates, the length of the mooring wire, and the wave length. It is found that, the transmission coefficient kt decreases with the increase of the relative breakwater width B/L, the number of plates n and the relative wire length l/h, while the reflection coefficient kr takes the opposite trend. Therefore, it is possible to achieve kt values smaller than 0.25 and kr values larger than 0.80 when B/L is larger than 0.25 for the case of l/h-1.5 and n=4. In addition, empirical equations used for estimating the transmission and reflection coefficients are developed by using the dimensionless analysis, regression analysis and measured data and verified by different theoretical and experimental results.展开更多
This study aims to investigate the possibility of using biopolymer(environmental friendly material) to enhance the mechanical behaviors of collapsible soil.Two types of biopolymers were(xanthan gum and guar gum) used ...This study aims to investigate the possibility of using biopolymer(environmental friendly material) to enhance the mechanical behaviors of collapsible soil.Two types of biopolymers were(xanthan gum and guar gum) used in this study due to their stable behaviors under severe conditions and their availability with reasonable prices.The experimental program focused on three major soil properties,i.e.compaction characterizations,collapsible potential and shear parameters.These three properties are essential in process of soil improvement.Different biopolymer concentrations were used in this study and the experimental program was performed at two curing periods(soon after mixing the soil with the biopolymer and after one week curing time).Shear parameters were measured for the treated specimens under both soaked and unsoaked conditions,while a collapsible potential test was performed under different mixing conditions(wet mix and dry mix).A numerical model was built to predict the behavior of the treated collapsible soil after and before water immersing.The results indicated that the ability of both xanthan gum and guar gum can be used as improvement materials for collapsible soil treatment.The collapsible potential has been reduced from 9%to 1%after mixing the soil with 2%biopolymer concentration in the wet case.After one week curing,the cohesion has been increased from 8.5 kPa to105 kPa by increasing the xanthan gum concentration from zero to 2%,leading to an overall improvement in soil shear strength.It also proves that the guar gum is superior to the xanthan gum.The shear strength of soil can be increased by about 30%when using the guar gum in comparison with the xanthan gum at the same conditions;however,the collapsible potential of soil material will be reduced by about 20%.展开更多
A numerical procedure for reliability analysis of earth slope based on advanced first-order second-moment method is presented,while soil properties and pore water pressure may be considered as random variables.The fac...A numerical procedure for reliability analysis of earth slope based on advanced first-order second-moment method is presented,while soil properties and pore water pressure may be considered as random variables.The factor of safety and performance function is formulated utilizing a new approach of the Morgenstern and Price method.To evaluate the minimum reliability index defined by Hasofer and Lind and corresponding critical probabilistic slip surface,a hybrid algorithm combining chaotic particle swarm optimization and harmony search algorithm called CPSOHS is presented.The comparison of the results of the presented method,standard particle swarm optimization,and selected other methods employed in previous studies demonstrates the superior successful functioning of the new method by evaluating lower values of reliability index and factor of safety.Moreover,the presented procedure is applied for sensitivity analysis and the obtained results show the influence of soil strength parameters and probability distribution types of random variables on the reliability index of slopes.展开更多
This paper introduces a new approach of firefly algorithm based on opposition-based learning （OBFA） to enhance the global search ability of the original algorithm. The new algorithm employs opposition based learning...This paper introduces a new approach of firefly algorithm based on opposition-based learning （OBFA） to enhance the global search ability of the original algorithm. The new algorithm employs opposition based learning concept to generate initial population and also updating agents’ positions. The proposed OBFA is applied for minimization of the factor of safety and search for critical failure surface in slope stability analysis. The numerical experiments demonstrate the effectiveness and robustness of the new algorithm.展开更多
Increased urbanisation,economic growth,and long-term climate variability have made both the UK and China more susceptible to urban and river flooding,putting people and property at increased risk.This paper presents a...Increased urbanisation,economic growth,and long-term climate variability have made both the UK and China more susceptible to urban and river flooding,putting people and property at increased risk.This paper presents a review of the current flooding challenges that are affecting the UK and China and the actions that each country is undertaking to tackle these problems.Particular emphases in this paper are laid on(1)learning from previous flooding events in the UK and China,and(2)which management methodologies are commonly used to reduce flood risk.The paper concludes with a strategic research plan suggested by the authors,together with proposed ways to overcome identified knowledge gaps in flood management.Recommendations briefly comprise the engagement of all stakeholders to ensure a proactive approach to land use planning,early warning systems,and water-sensitive urban design or redesign through more effective policy,multi-level flood models,and data driven models of water quantity and quality.展开更多
A new method is proposed to assess the condition of structures under unknown support excitation by simultaneously detecting local damage and identifying the support excitation from several structural dynamic responses...A new method is proposed to assess the condition of structures under unknown support excitation by simultaneously detecting local damage and identifying the support excitation from several structural dynamic responses. The support excitation acting on a structure is modeled by orthogonal polynomial approximations, and the sensitivities of structural dynamic response with respect to its physical parameters and orthogonal coefficients are derived. The identification equation is based on Taylor＇s first order approximation, and is solved with the damped least-squares method in an iterative procedure. A fifteen-story shear building model and a five-story three-dimensional steel frame structure are studied to validate the proposed method. Numerical simulations with noisy measured accelerations show that the proposed method can accurately detect local damage and identify unknown support excitation from only several responses of the structure. This method provides a new approach for detecting structural damage and updating models with unknown input and incomplete measured output information.展开更多
A new hybrid optimization algorithm was presented by integrating the gravitational search algorithm （GSA） with the sequential quadratic programming （SQP）, namely GSA-SQP, for solving global optimization problems a...A new hybrid optimization algorithm was presented by integrating the gravitational search algorithm （GSA） with the sequential quadratic programming （SQP）, namely GSA-SQP, for solving global optimization problems and minimization of factor of safety in slope stability analysis. The new algorithm combines the global exploration ability of the GSA to converge rapidly to a near optimum solution. In addition, it uses the accurate local exploitation ability of the SQP to accelerate the search process and find an accurate solution. A set of five well-known benchmark optimization problems was used to validate the performance of the GSA-SQP as a global optimization algorithm and facilitate comparison with the classical GSA. In addition, the effectiveness of the proposed method for slope stability analysis was investigated using three ease studies of slope stability problems from the literature. The factor of safety of earth slopes was evaluated using the Morgenstern-Price method. The numerical experiments demonstrate that the hybrid algorithm converges faster to a significantly more accurate final solution for a variety of benchmark test functions and slope stability problems.展开更多
Seismic codes estimate the maximum displacements of building structures under the design-basis earthquakes by amplifying the elastic displacements under the reduced seismic design forces with a deflection amplificatio...Seismic codes estimate the maximum displacements of building structures under the design-basis earthquakes by amplifying the elastic displacements under the reduced seismic design forces with a deflection amplification factor(DAF). The value of DAF is often estimated as ρ× R, where R is the force reduction factor and ρ is the inelastic displacement ratio that accounts for the inelastic action of the structure according to the definition presented by FEMA P695. The purpose of this study is to estimate the ρ-ratio of moment resisting steel frames(MRSFs) designed according to the Egyptian code. This is achieved by conducting a series of elastic and inelastic time-history analyses by two sets of earthquakes on four MRSFs designed according to the Egyptian code and having 2, 4, 8 and 12 stories. The earthquakes are scaled to produce maximum story drift ratios(MSDRs) of 1.0%, 1.5%, 2.0% and 2.5%. The mean values of the ρ-ratio are calculated based on the displacement responses of the investigated frames. The results obtained in this study indicate that the consideration of ρ for both the roof drift ratios(RDRs) and the MSDRs equal to 1.0 is a reasonable estimation for MRSFs designed according to the Egyptian code.展开更多
With the opening of ancient Tibetan structures to visitors worldwide, human load has become the principal live load on these structures. This project studies the properties of the floor structure of an ancient Tibetan...With the opening of ancient Tibetan structures to visitors worldwide, human load has become the principal live load on these structures. This project studies the properties of the floor structure of an ancient Tibetan building and its behavior under human-induced load effects. Tests were conducted with static and dynamic crowd load, including stepping and jogging by people at a fixed position. The tests show that the floor structure does not behave as a continuous slab. It takes the load from local areas with minimal load transference properties. The acceleration response shows significant peaks when the footstep frequency is close to the natural frequency of the s~＇ucture, but the human jogging excitation frequency does not have any obvious effect on the structural response. The elastic modulus of the Agatu material is estimated to be close to zero from the measured natural frequency of the slab. The Agatu material is concluded to be a discrete compacted material with insignificant contribution to the structural rigidity of the floor slab.展开更多
Chloride ion critical content was studied under soaking and cycle of dry and wet conditions, with three electrochemical nondestructive measuring techniques, i e, half-cell potential, A C impedance, and time potential....Chloride ion critical content was studied under soaking and cycle of dry and wet conditions, with three electrochemical nondestructive measuring techniques, i e, half-cell potential, A C impedance, and time potential. The experimental results show that chloride ion critical content is primarily determined by the water cement ratio, while for the same concrete mixture the chloride ion critical content in soaking conditions is larger than that in a cycle of dry and wet conditions.展开更多
Rockburst is an important phenomenon that has affected many deep underground mines around the world. An understanding of this phenomenon is relevant to the management of such events, which can lead to saving both cost...Rockburst is an important phenomenon that has affected many deep underground mines around the world. An understanding of this phenomenon is relevant to the management of such events, which can lead to saving both costs and lives. Laboratory experiments are one way to obtain a deeper and better understanding of the mechanisms of rockburst. In a previous study by these authors, a database of rockburst laboratory tests was created; in addition, with the use of data mining （DM） techniques, models to predict rockburst maximum stress and rockburst risk indexes were developed. In this paper, we focus on the analysis of a database of in situ cases of rockburst in order to build influence diagrams, list the factors that interact in the occurrence of rockburst, and understand the relationships between these factors. The in situ rockburst database was further analyzed using different DM techniques ranging from artificial neural networks （ANNs） to naive Bayesian classifiers. The aim was to predict the type of rockburst-that is, the rockburst level-based on geologic and construction characteristics of the mine or tunnel. Conclusions are drawn at the end of the paper.展开更多
In this study, inelastic nonlinear pushover analysis is performed on a 3-D model of a jacket-type offshore platform for the North Sea conditions. The structure＇ is modelled, analyzed and designed using finite element...In this study, inelastic nonlinear pushover analysis is performed on a 3-D model of a jacket-type offshore platform for the North Sea conditions. The structure＇ is modelled, analyzed and designed using finite element software SACS （structural analysis computer system）. The behavior of jackets with different bracing systems under pushover analysis is examined. Further, by varying the leg batter values of the platform, weight optimization is carried-out. Soil-structure interaction effect is considered in the analyses and the results are compared with the hypothetical fixed-support end condition. Static and dynamic pushover analyses are performed by using wave and seismic loads respectively. From the analyses, it is found that the optimum leg batter varies between 15 to 16 and 2% of weight saving is achieved. Moreover, it has been observed that the type of bracing does not play a major role in the seismic design of jacket platform considering the soil-structure interaction.展开更多
Herein,iron oxide/hydroxides deposits(gossans)were utilized,for the first time,in the fabrication of magnetite nanoparticles(MNPs)to load modified coal(MC).The as-synthesized MNPs@MC composite was characterized via di...Herein,iron oxide/hydroxides deposits(gossans)were utilized,for the first time,in the fabrication of magnetite nanoparticles(MNPs)to load modified coal(MC).The as-synthesized MNPs@MC composite was characterized via different techniques and utilized for the Cr(Ⅵ)remediation.Experimental studies supported by theoretical treatment were applied to offer a new overview of the Cr(Ⅵ)adsorption geometry and mechanism at 25-45℃.Experimental results suggested that the Cr(Ⅵ)uptake was mainly governed by adsorption-reduction coupled mechanism.The Langmuir model fitted well the Cr(Ⅵ)adsorption data with maximum adsorption capacities extended from 115.24 to 129.63 mg·g^(-1).Theoretical calculations indicated that Cr(Ⅵ)ions were adsorbed on the MNPs@MC following the theory of the advanced monolayer statistical model.The number of ions removed per site ranged from 1.88 to1.23 suggesting the involvement of vertical geometry and multi-ionic mechanism at all temperatures.The increment of the active sites density and the adsorption capacity at saturation with improving temperature reflected an endothermic process.Energetically,the Cr(Ⅵ)adsorption was controlled by physical forces as the adsorption energies were less than 40 kJ·mol^(-1).The calculated free enthalpy,entropy.and internal energy explained the spontaneous nature and the viability of Cr(Ⅵ)adsorption on the MNPs@MC adsorbent.These results offer a new approach in utilizing the iron-rich deposits as gossans in the preparation of magnetic and low-cost adsorbents for wastewater remediation.展开更多
The competitive trends of the world market have long been forcing structural engineers to develop minimum weight and labour cost solutions. A direct consequence of this new design trend has been a considerable increas...The competitive trends of the world market have long been forcing structural engineers to develop minimum weight and labour cost solutions. A direct consequence of this new design trend has been a considerable increase in problems related to undesired floor vibrations. For this reason, structural floor systems can become vulnerable to excessive vibrations that are produced by, for example, impacts due to mechanical equipment （e.g., rotating machinery）. This study investigates the dynamic behaviour of a production platform constructed of steel and located in the Santos Basin （Merluza field）, Sao Paulo/SP, Brazil, when subjected to impacts produced by mechanical equipment （rotating machinery）. The structural model consists of two steel decks with a total area of 1,915 m^2 （upper deck： 445 m^2, lower deck： 1,470 m^2） and supported by piles. A numerical analysis is performed to assess the dynamic impacts on the deck structure originating from the electrical generators and compressors. Based on the peak acceleration values obtained for the structure steady-state response, it is possible to evaluate the structural model performance in terms of human comfort, the maximum tolerances of the mechanical equipment and the vibration serviceability limit states of the structure.展开更多
A three dimensional finite element of nonlinear pushover analysis for short span Reinforced Concrete (RC) bridge with circular piers cross section is modeling to present effects of soil structural interaction (SSI). S...A three dimensional finite element of nonlinear pushover analysis for short span Reinforced Concrete (RC) bridge with circular piers cross section is modeling to present effects of soil structural interaction (SSI). Structural elements models are including linear foundation springs modeling, and nonlinear RC piers modeling. The paper succeeded to present the SSI effects of nonlinear pushover analysis of short spans RC bridges to determine the significant effects on dynamic characteristics and displacement capacity of short span RC bridges performance;that is increasing within range 11% to 20% compared to baseline pushover analysis of bridge without SSI effects. Results show the bridge stiffness decreases due to SSI effects on the bridge support for more flexible soils types that generates large displacement, with corresponding less base shear in bridge piers and footings by average percentage 12% and 18%, which is important for structural evaluation for new bridge construction and also, for strengthening and repair works evaluation of existing bridges.展开更多
Height limitations are not uncommon in multi-storey buildings due to economic requirements and esthetical considerations. Substantial spaces are normally required to enable the passage of large pipes and ducts beneath...Height limitations are not uncommon in multi-storey buildings due to economic requirements and esthetical considerations. Substantial spaces are normally required to enable the passage of large pipes and ducts beneath steel beams leading to uneconomic floor heights. The most adopted solution for this issue is the use of steel beam web openings to provide the required space for services. These openings could lead to a significant decrease of the beam load carrying capacity depending on the adopted openings shape, size and location. These aspects motivated the present study based on FE simulations calibrated against numerical and test results. The results accuracy enabled a comprehensive parametric analysis of beams with web openings to be made focused on the profile size, web opening location, among others. The study also investigated the efficiency of longitudinal stiffeners welded at the opening region and benefits of using an adequate edge concordance radius in beams with rectangular and square openings. The obtained results showed the need of using welded longitudinal stiffeners in order to increase the beams ultimate load carrying capacity. This adoption can double or even triple the ultimate load of beams with rectangular and square opening heights equal to 0.75 H, respectively.展开更多
文摘This work aims the deterministic dynamic analysis,in the time and frequency domain,of a reinforced concrete floor supported by a pre-cast pile foundation system,when subjected to the excitation produced by a large compressor installed in an industry for the production of air gases.The concrete slab presents a dimension of 12 m×15 m,required to support a compressor-motor assembly weighting 1,900 kN and positioned at a height of 4m of the investigated concrete floor.In this investigation,two numerical models were developed and the difference between these models is characterized by the discretization of the support points(pre-cast concrete piles).The developed numerical model adopted the usual mesh refinement techniques present in finite element method simulations implemented in the CSi SAP2000 V.17.2.0 software.Based on the developed analysis methodology,the dynamic structural response of the foundation system is evaluated in terms of natural frequencies,vibration modes,displacements,velocities,and accelerations.The maximum values of the dynamic response of the system are compared with the limit values recommended by standards and project recommendations,aiming a careful evaluation,regarding the performance of the structure in terms of excessive vibrations and the economic aspects involved in the design of the foundation system.Finally,the obtained results of the two developed numerical models are compared,as to evaluate if there are benefits in refining the support points modelling.
文摘Purpose of present work is to develop a reliable and simple method for structural analysis of RC Shear Walls. The shear wall is simulated by a truss model as the bar of a truss is the simplest finite element. An iterative method is used. Initially, there are only concrete bars. Repeated structural analyses are performed. After each structural analysis, every concrete bar exceeding tensile strength is replaced by a steel bar. For every concrete bar exceeding compressive strength, first its section area is increased. If this is not enough, a steel bar is placed at the side of it. For every steel bar exceeding tensile or compressive strength, its section area is increased. After the end of every structural analysis, if all concrete and steel bars fall within tensile and compressive strengths, the output data are written and the analysis is terminated. Otherwise, the structural analysis is repeated. As all the necessary conditions (static, elastic, linearized geometric) are satisfied and the stresses of ALL concrete and steel bars fall within the tensile and compressive strengths, the results are acceptable. Usually, the proposed method exhibits a fast convergence in 4 - 5 repeats of structural analysis of the RC Shear Wall.
基金from Sandooq al Watan is acknowledged(No.ADHPG-S1570)This work was partially supported by the Sand Hazards and Opportunities for Resilience,Energy,and Sustainability(SHORES)Center,funded by Tamkeen under the NYUAD Research Institute Award CG013The authors also acknowledge the Mohammed Bin Rashid Space Centre’s(MBRSC)Emirates Lunar Mission(EML)group’s continued support in making the research project successful.
文摘Lunar soil simulants(LSS)have been pivotal in the success of past and current lunar missions.They have enhanced the design of lander and rover wheels through interaction studies on the lunar testbed under simulated environmental conditions.They have also been used to evaluate the geotechnical,geomechanical,and dynamic characteristics of the lunar soil(LS),which is vital for future lunar outposts.While most simulants have focused on either the chemical and mineralogical or geotechnical properties,developing a comprehensive LSS that mimics the lunar soil is of paramount importance for lander and rover soft-landing and future lunar habitation.This article presents the significant development and characterization of the new LSS NYUAD-1,the first regional soil simulant tailored for the planned Emirates lunar missions.The material and geotechnical properties of NYUAD-1,including chemical composition,mineralogy,particle size,morphology,specific gravity,density,shear strength,and compressibility behaviors,were assessed through laboratory tests conducted per ASTM standards.Comparative analysis with authentic lunar regolith and various regolith simulants confirms the significance and applicability of NYUAD-1 for lunar-based research,offering a promising step toward future lunar habitation.
文摘A dynamic analysis of both twisting and regular towers is carried out to determine the results of considering soil-structure interaction(SSI)on high-rise buildings.In addition,the difference between the seismic performance of using twisting towers over regular ones is investigated.The twisting tower is a simulation of the Evolution Tower(Moscow).The towers’skeletons consist of RC elements and rest on a reinforced concrete piled-raft foundation.The soil model is considered as multi-layered with the same soil properties as the zone chosen for the analysis(New Mansoura City,Egypt).The only difference between both towers is their shape in elevation.The whole system is modelled and analyzed in a single step as one full 3D model,which is known as the direct approach in SSI.All analyses are carried out using finite-element software(Midas GTS NX).Dynamic output responses due to three records of seismic loads are proposed and presented in some graphs.Based on the results,it is concluded that SSI has a considerable effect on the dynamic response of tall buildings mainly because of the foundation flexibility,as it leads to lengthening the vibration period,increasing the story drift and the base shear for both cases.
文摘In this paper, the hydrodynamic efficiency of a floating breakwater system is experimentally studied by use of physical models. Regular waves with wide ranges of wave heights and periods are tested. The efficiency of the breakwater is presented as a function of the wave transmission, reflection, and energy dissipation coefficients. Different parameters affecting the breakwater efficiency are investigated, e.g. the number of the under connected vertical plates, the length of the mooring wire, and the wave length. It is found that, the transmission coefficient kt decreases with the increase of the relative breakwater width B/L, the number of plates n and the relative wire length l/h, while the reflection coefficient kr takes the opposite trend. Therefore, it is possible to achieve kt values smaller than 0.25 and kr values larger than 0.80 when B/L is larger than 0.25 for the case of l/h-1.5 and n=4. In addition, empirical equations used for estimating the transmission and reflection coefficients are developed by using the dimensionless analysis, regression analysis and measured data and verified by different theoretical and experimental results.
文摘This study aims to investigate the possibility of using biopolymer(environmental friendly material) to enhance the mechanical behaviors of collapsible soil.Two types of biopolymers were(xanthan gum and guar gum) used in this study due to their stable behaviors under severe conditions and their availability with reasonable prices.The experimental program focused on three major soil properties,i.e.compaction characterizations,collapsible potential and shear parameters.These three properties are essential in process of soil improvement.Different biopolymer concentrations were used in this study and the experimental program was performed at two curing periods(soon after mixing the soil with the biopolymer and after one week curing time).Shear parameters were measured for the treated specimens under both soaked and unsoaked conditions,while a collapsible potential test was performed under different mixing conditions(wet mix and dry mix).A numerical model was built to predict the behavior of the treated collapsible soil after and before water immersing.The results indicated that the ability of both xanthan gum and guar gum can be used as improvement materials for collapsible soil treatment.The collapsible potential has been reduced from 9%to 1%after mixing the soil with 2%biopolymer concentration in the wet case.After one week curing,the cohesion has been increased from 8.5 kPa to105 kPa by increasing the xanthan gum concentration from zero to 2%,leading to an overall improvement in soil shear strength.It also proves that the guar gum is superior to the xanthan gum.The shear strength of soil can be increased by about 30%when using the guar gum in comparison with the xanthan gum at the same conditions;however,the collapsible potential of soil material will be reduced by about 20%.
基金supported by the Ministry of Higher Education, Malaysia (Grant No.UKM-AP-PLW-04-2009/2)
文摘A numerical procedure for reliability analysis of earth slope based on advanced first-order second-moment method is presented,while soil properties and pore water pressure may be considered as random variables.The factor of safety and performance function is formulated utilizing a new approach of the Morgenstern and Price method.To evaluate the minimum reliability index defined by Hasofer and Lind and corresponding critical probabilistic slip surface,a hybrid algorithm combining chaotic particle swarm optimization and harmony search algorithm called CPSOHS is presented.The comparison of the results of the presented method,standard particle swarm optimization,and selected other methods employed in previous studies demonstrates the superior successful functioning of the new method by evaluating lower values of reliability index and factor of safety.Moreover,the presented procedure is applied for sensitivity analysis and the obtained results show the influence of soil strength parameters and probability distribution types of random variables on the reliability index of slopes.
文摘This paper introduces a new approach of firefly algorithm based on opposition-based learning （OBFA） to enhance the global search ability of the original algorithm. The new algorithm employs opposition based learning concept to generate initial population and also updating agents’ positions. The proposed OBFA is applied for minimization of the factor of safety and search for critical failure surface in slope stability analysis. The numerical experiments demonstrate the effectiveness and robustness of the new algorithm.
基金supported by the National Key Research and Development Program of China(Grant No.2016YFE0122500)the Researcher Links Fund,British Council(Grant No.227109770)+1 种基金the National Natural Science Foundation of China(Grants No.5151101425 and 51579166)the Open Research Fund from the State Key Laboratory of Hydraulics and Mountain River Engineering,Sichuan University(Grants No.SKHL1601 and SKHL1602)
文摘Increased urbanisation,economic growth,and long-term climate variability have made both the UK and China more susceptible to urban and river flooding,putting people and property at increased risk.This paper presents a review of the current flooding challenges that are affecting the UK and China and the actions that each country is undertaking to tackle these problems.Particular emphases in this paper are laid on(1)learning from previous flooding events in the UK and China,and(2)which management methodologies are commonly used to reduce flood risk.The paper concludes with a strategic research plan suggested by the authors,together with proposed ways to overcome identified knowledge gaps in flood management.Recommendations briefly comprise the engagement of all stakeholders to ensure a proactive approach to land use planning,early warning systems,and water-sensitive urban design or redesign through more effective policy,multi-level flood models,and data driven models of water quantity and quality.
基金National Natural Science Foundation of China Under Grant No.50579008Joint Research Fund for Overseas Chinese, Hong Kong and Macao Young Scholars Under Grant No.50429802+1 种基金Program for New Century Excellent Talents in University by State Education Commission Under Grant No.NCET-04-0323a research grant from the Hong Kong Polytechnic University
文摘A new method is proposed to assess the condition of structures under unknown support excitation by simultaneously detecting local damage and identifying the support excitation from several structural dynamic responses. The support excitation acting on a structure is modeled by orthogonal polynomial approximations, and the sensitivities of structural dynamic response with respect to its physical parameters and orthogonal coefficients are derived. The identification equation is based on Taylor＇s first order approximation, and is solved with the damped least-squares method in an iterative procedure. A fifteen-story shear building model and a five-story three-dimensional steel frame structure are studied to validate the proposed method. Numerical simulations with noisy measured accelerations show that the proposed method can accurately detect local damage and identify unknown support excitation from only several responses of the structure. This method provides a new approach for detecting structural damage and updating models with unknown input and incomplete measured output information.
文摘A new hybrid optimization algorithm was presented by integrating the gravitational search algorithm （GSA） with the sequential quadratic programming （SQP）, namely GSA-SQP, for solving global optimization problems and minimization of factor of safety in slope stability analysis. The new algorithm combines the global exploration ability of the GSA to converge rapidly to a near optimum solution. In addition, it uses the accurate local exploitation ability of the SQP to accelerate the search process and find an accurate solution. A set of five well-known benchmark optimization problems was used to validate the performance of the GSA-SQP as a global optimization algorithm and facilitate comparison with the classical GSA. In addition, the effectiveness of the proposed method for slope stability analysis was investigated using three ease studies of slope stability problems from the literature. The factor of safety of earth slopes was evaluated using the Morgenstern-Price method. The numerical experiments demonstrate that the hybrid algorithm converges faster to a significantly more accurate final solution for a variety of benchmark test functions and slope stability problems.
文摘Seismic codes estimate the maximum displacements of building structures under the design-basis earthquakes by amplifying the elastic displacements under the reduced seismic design forces with a deflection amplification factor(DAF). The value of DAF is often estimated as ρ× R, where R is the force reduction factor and ρ is the inelastic displacement ratio that accounts for the inelastic action of the structure according to the definition presented by FEMA P695. The purpose of this study is to estimate the ρ-ratio of moment resisting steel frames(MRSFs) designed according to the Egyptian code. This is achieved by conducting a series of elastic and inelastic time-history analyses by two sets of earthquakes on four MRSFs designed according to the Egyptian code and having 2, 4, 8 and 12 stories. The earthquakes are scaled to produce maximum story drift ratios(MSDRs) of 1.0%, 1.5%, 2.0% and 2.5%. The mean values of the ρ-ratio are calculated based on the displacement responses of the investigated frames. The results obtained in this study indicate that the consideration of ρ for both the roof drift ratios(RDRs) and the MSDRs equal to 1.0 is a reasonable estimation for MRSFs designed according to the Egyptian code.
基金National Natural Science Foundation of China Under Grant No.51178028 and No.50938008Program for New Century Excellent Talents in University(NCET-11-0571)+1 种基金the Fundamental Research Funds for the Central Universities(2012JBM007)the 111 Project(B13002)
文摘With the opening of ancient Tibetan structures to visitors worldwide, human load has become the principal live load on these structures. This project studies the properties of the floor structure of an ancient Tibetan building and its behavior under human-induced load effects. Tests were conducted with static and dynamic crowd load, including stepping and jogging by people at a fixed position. The tests show that the floor structure does not behave as a continuous slab. It takes the load from local areas with minimal load transference properties. The acceleration response shows significant peaks when the footstep frequency is close to the natural frequency of the s~＇ucture, but the human jogging excitation frequency does not have any obvious effect on the structural response. The elastic modulus of the Agatu material is estimated to be close to zero from the measured natural frequency of the slab. The Agatu material is concluded to be a discrete compacted material with insignificant contribution to the structural rigidity of the floor slab.
文摘Chloride ion critical content was studied under soaking and cycle of dry and wet conditions, with three electrochemical nondestructive measuring techniques, i e, half-cell potential, A C impedance, and time potential. The experimental results show that chloride ion critical content is primarily determined by the water cement ratio, while for the same concrete mixture the chloride ion critical content in soaking conditions is larger than that in a cycle of dry and wet conditions.
文摘Rockburst is an important phenomenon that has affected many deep underground mines around the world. An understanding of this phenomenon is relevant to the management of such events, which can lead to saving both costs and lives. Laboratory experiments are one way to obtain a deeper and better understanding of the mechanisms of rockburst. In a previous study by these authors, a database of rockburst laboratory tests was created; in addition, with the use of data mining （DM） techniques, models to predict rockburst maximum stress and rockburst risk indexes were developed. In this paper, we focus on the analysis of a database of in situ cases of rockburst in order to build influence diagrams, list the factors that interact in the occurrence of rockburst, and understand the relationships between these factors. The in situ rockburst database was further analyzed using different DM techniques ranging from artificial neural networks （ANNs） to naive Bayesian classifiers. The aim was to predict the type of rockburst-that is, the rockburst level-based on geologic and construction characteristics of the mine or tunnel. Conclusions are drawn at the end of the paper.
文摘In this study, inelastic nonlinear pushover analysis is performed on a 3-D model of a jacket-type offshore platform for the North Sea conditions. The structure＇ is modelled, analyzed and designed using finite element software SACS （structural analysis computer system）. The behavior of jackets with different bracing systems under pushover analysis is examined. Further, by varying the leg batter values of the platform, weight optimization is carried-out. Soil-structure interaction effect is considered in the analyses and the results are compared with the hypothetical fixed-support end condition. Static and dynamic pushover analyses are performed by using wave and seismic loads respectively. From the analyses, it is found that the optimum leg batter varies between 15 to 16 and 2% of weight saving is achieved. Moreover, it has been observed that the type of bracing does not play a major role in the seismic design of jacket platform considering the soil-structure interaction.
基金supported by Researchers Supporting Project number(RSP2023R455),King Saud University,Riyadh,Saudi Arabia。
文摘Herein,iron oxide/hydroxides deposits(gossans)were utilized,for the first time,in the fabrication of magnetite nanoparticles(MNPs)to load modified coal(MC).The as-synthesized MNPs@MC composite was characterized via different techniques and utilized for the Cr(Ⅵ)remediation.Experimental studies supported by theoretical treatment were applied to offer a new overview of the Cr(Ⅵ)adsorption geometry and mechanism at 25-45℃.Experimental results suggested that the Cr(Ⅵ)uptake was mainly governed by adsorption-reduction coupled mechanism.The Langmuir model fitted well the Cr(Ⅵ)adsorption data with maximum adsorption capacities extended from 115.24 to 129.63 mg·g^(-1).Theoretical calculations indicated that Cr(Ⅵ)ions were adsorbed on the MNPs@MC following the theory of the advanced monolayer statistical model.The number of ions removed per site ranged from 1.88 to1.23 suggesting the involvement of vertical geometry and multi-ionic mechanism at all temperatures.The increment of the active sites density and the adsorption capacity at saturation with improving temperature reflected an endothermic process.Energetically,the Cr(Ⅵ)adsorption was controlled by physical forces as the adsorption energies were less than 40 kJ·mol^(-1).The calculated free enthalpy,entropy.and internal energy explained the spontaneous nature and the viability of Cr(Ⅵ)adsorption on the MNPs@MC adsorbent.These results offer a new approach in utilizing the iron-rich deposits as gossans in the preparation of magnetic and low-cost adsorbents for wastewater remediation.
基金Acknowledgments The authors gratefully acknowledge the support for this work provided by the Brazilian Science Foundations： CAPES, CNPq and FAPERJ.
文摘The competitive trends of the world market have long been forcing structural engineers to develop minimum weight and labour cost solutions. A direct consequence of this new design trend has been a considerable increase in problems related to undesired floor vibrations. For this reason, structural floor systems can become vulnerable to excessive vibrations that are produced by, for example, impacts due to mechanical equipment （e.g., rotating machinery）. This study investigates the dynamic behaviour of a production platform constructed of steel and located in the Santos Basin （Merluza field）, Sao Paulo/SP, Brazil, when subjected to impacts produced by mechanical equipment （rotating machinery）. The structural model consists of two steel decks with a total area of 1,915 m^2 （upper deck： 445 m^2, lower deck： 1,470 m^2） and supported by piles. A numerical analysis is performed to assess the dynamic impacts on the deck structure originating from the electrical generators and compressors. Based on the peak acceleration values obtained for the structure steady-state response, it is possible to evaluate the structural model performance in terms of human comfort, the maximum tolerances of the mechanical equipment and the vibration serviceability limit states of the structure.
文摘A three dimensional finite element of nonlinear pushover analysis for short span Reinforced Concrete (RC) bridge with circular piers cross section is modeling to present effects of soil structural interaction (SSI). Structural elements models are including linear foundation springs modeling, and nonlinear RC piers modeling. The paper succeeded to present the SSI effects of nonlinear pushover analysis of short spans RC bridges to determine the significant effects on dynamic characteristics and displacement capacity of short span RC bridges performance;that is increasing within range 11% to 20% compared to baseline pushover analysis of bridge without SSI effects. Results show the bridge stiffness decreases due to SSI effects on the bridge support for more flexible soils types that generates large displacement, with corresponding less base shear in bridge piers and footings by average percentage 12% and 18%, which is important for structural evaluation for new bridge construction and also, for strengthening and repair works evaluation of existing bridges.
文摘Height limitations are not uncommon in multi-storey buildings due to economic requirements and esthetical considerations. Substantial spaces are normally required to enable the passage of large pipes and ducts beneath steel beams leading to uneconomic floor heights. The most adopted solution for this issue is the use of steel beam web openings to provide the required space for services. These openings could lead to a significant decrease of the beam load carrying capacity depending on the adopted openings shape, size and location. These aspects motivated the present study based on FE simulations calibrated against numerical and test results. The results accuracy enabled a comprehensive parametric analysis of beams with web openings to be made focused on the profile size, web opening location, among others. The study also investigated the efficiency of longitudinal stiffeners welded at the opening region and benefits of using an adequate edge concordance radius in beams with rectangular and square openings. The obtained results showed the need of using welded longitudinal stiffeners in order to increase the beams ultimate load carrying capacity. This adoption can double or even triple the ultimate load of beams with rectangular and square opening heights equal to 0.75 H, respectively.
